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The Königsberg Bridge Problem. Leonhard “my name rhymes with boiler” Euler (1707-1783).
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“The problem, which I understand is quite well known, is stated as follows: In the town of Könisberg in Prussia there is an island called Kneiphof, with two branches of the river Pregel flowing around it. There are 7 bridges - a, b, c, d, e, f, and g - crossing the two branches. The question is whether a person can plan a walk in such a way that he will cross each of these bridges once but not more than once. I was told that while some denied the possibility of doing this and others were in doubt, no one maintained that it was actually possible. On the basis of the above I formulated the following very general problem.....”
a b c d e g f
a b c d g f e
R A B L
R a b c A d B e g f L
R A B L
R a A
R A
R A B L
R R R A
R A B L
R R R A A A B B A A B L L L
R R R B A B B L L L
R R R B A B B L L L
R B A B B L L L
R B A B B L L L
R A B L L L
R A B L L L
R A B L
R A B L
The resulting figure is called a graph. The dots are its vertices and the lines are its edges. Leonard Euler was able to solve the Königsberg Bridge Problem by first modeling it with this graph.
R A B L
Can we trace all the edges in Euler’s graph without retracing any? If yes, how? If not, why not?